Abstract

Cold-water coral (CWC) reefs constitute one of the most complex deep-sea habitats harboring a vast diversity of associated species. Like other tropical or temperate framework builders, these systems are facing an uncertain future due to several threats, such as global warming and ocean acidification. In the case of Mediterranean CWC communities, the effect may be exacerbated due to the greater capacity of these waters to absorb atmospheric CO2 compared to the global ocean. Calcification in these organisms is an energy-demanding process, and it is expected that energy requirements will be greater as seawater pH and the availability of carbonate ions decrease. Therefore, studies assessing the effect of a pH decrease in skeletal growth, and metabolic balance are critical to fully understand the potential responses of these organisms under a changing scenario. In this context, the present work aims to investigate the medium- to long-term effect of a low pH scenario on calcification and the biochemical composition of two CWCs from the Mediterranean, Dendrophyllia cornigera and Desmophyllum dianthus. After 314 d of exposure to acidified conditions, a significant decrease of 70 % was observed in Desmophyllum dianthus skeletal growth rate, while Dendrophyllia cornigera showed no differences between treatments. Instead, only subtle differences between treatments were observed in the organic matter amount, lipid content, skeletal microdensity, or porosity in both species, although due to the high variability of the results, these differences were not statistically significant. Our results also confirmed a heterogeneous effect of low pH on the skeletal growth rate of the organisms depending on their initial weight, suggesting that those specimens with high calcification rates may be the most susceptible to the negative effects of acidification.

Notes

Acknowledgments

We want to thank A. Olariaga for his suggestions during the experimental setup, to M. Dalmau, F. X. Capdevila, and L. Pedret, for helping with coral maintenance, to M. Delgado (ZAE, ICM) for technical assistances and to the Marine Technology Unit (UTM, CSIC), M. Taviani (ISMAR-CNR, Bologna) and the crews of RVs ‘Urania,’ ‘Garcia del Cid’ and the ‘JAGO-Team’ (IFM-GEOMAR) for their support during coral collection. We are also in debt with P. Siles for valuable advice in coral maintenance and behavior. Constructive comments by C. Maier and an anonymous reviewer greatly improved this paper. This research was supported by the European Projects HERMES (Goce-CT-2005-511234-I), HERMIONE (Grant Agreement Number 226354), the Spanish Projects CTM2009-08849/MAR and CTM2012-32017 and by the Marine Biogeochemistry and Global Change research group (Generalitat de Catalunya, 2009SGR142). J.M. was funded by a FPI studentship (BES-2007-16537) and A.G. by an I3P studentship (Ref. I3P-BPD2005) from the Spanish Government. The experiment was performed at the Zona de Acuarios Experimentales (ZAE) of ICM-CSIC.

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